Gliederung

Introduction: Gastric cancer represents the second largest cause of cancer-related deaths worldwide. The transcription factor HIF-1α, the main regulator of cellular adaptation to hypoxia, appears to contribute to gastric cancer pathogenesis. The underlying mechanisms, however, have yet not been clarified. Transition of epithelial cancer cells to a mesenchymal, i.e. motile and invasive phenotype (epithelial-mesenchymal transition, EMT) is thought to facilitate gastric cancer metastasis. Therefore, we investigated the role of HIF-1α in mediating gastric cancer cell motility.

Methods: Expression of HIF-1α was analyzed by immunohistochemistry in tissue microarrays of 45 human gastric cancer samples and corresponding healthy control tissues. The influence of functional inactivation of HIF-1α on proliferation, survival and migration of gastric cancer cells was studied using the AGS cell model. Inactivation of HIF-1α was achieved by transient transfection as well as stable lentiviral transfer of short interfering RNA. The HIF-1α status of AGS cells was monitored by western blot analysis.

Results: 89% (40/45) of gastric cancer samples displayed expression of HIF-1α in >90% of neoplastic cells, whereas in controls HIF-1α protein abundance never exceeded 20% of total epithelial cells. 80% of control samples displayed HIF-1αpositivity, with parietal cells being the principle source of HIF-1α protein. Proliferation and survival of AGS cells under normoxia was not affected by inactivating HIF-1α. However, migration of AGS cells was reduced to at least 40% of wild type levels after HIF-1α knock-down. Addition of excess free ATP did not revert the reduced migration of HIF-1α-deficient AGS cells indicating that the observed phenotype can not be explained by defective energy generation.

Conclusion: Our analysis of tumor samples shows that broad epithelial expression of HIF-1α is a frequent and prominent feature of human gastric adenocarcinomas. Moreover, for the first time we present experimental evidence that HIF-1α acts as a regulator of gastric cancer cell motility. Our results suggest that HIF-1α may support the initial steps of EMT and thereby the acquisition of a metastatic phenotype of gastric cancer cells.